The present invention relates generally to a technique for sealing an end of an optical fiber to a metal component. This subsequently enables the making of a spliced connection between lengths of optical fibers.
The application of fiber optics for a particular use is dependent on the requirement of being able to connect or splice one length of glass fiber to another length. These connections have, in the past, been performed in a number of ways.
Methods of sealing an optical fiber with a metal have used ferrules to clamp or glue the fibers together. These ferrules then are optically aligned in a mechanical process. Another known method is to pass the fiber through a threaded nut, glue or solder the fiber to the nut and then attach the nut to the assembly. These methods produced non-hermetic seals which contained cracks. A third previously used method was the Fiber Insertion Technique of U.S. Pat. No. 5,143,531. This method requires the heat source to be removed while the fiber optic is inserted into the previously heated molten glass. However, it is difficult to accurately place the fiber within the molten glass. None of these prior methods provide a connection or splice which is hermetic to the degree that is necessary for certain types of components which require a helium leak rate of less than 1.times.10.sup.-8 cm.sup.3 /sec.
Other problems occur in sealing the fiber to the metal component since the fibers are usually coated in a protective coating buffer. Without this buffer, the fibers are easily broken, but with these buffers, which are usually made of plastic, the fibers cannot withstand the high temperatures used for the sealing. The glass fibers themselves are typically thin (approximately 0.008 inch wide) so that they will also deform and lose strength at the high temperatures required for sealing. In addition, the differences in the thermal expansion coefficients of the optical fibers and the metal components further complicate the development of the fiber optic components, since most optical fibers have very low coefficients of thermal expansion (i.e., less than 10.times.10.sup.-7 cm/cm/.degree. C. between room temperature and 300.degree. C.) while certain metals, such as high-strength superalloys used in fiber optic components, typically have very large coefficients of thermal expansion (i.e., about 145.times.10.sup.-7 cm/cm/.degree. C. between room temperature and 300.degree. C.). This mismatch of thermal expansions causes cracks in the fibers and around the fibers. Furthermore, other problems have occurred causing loss of light from cracks when joining the lengths of the fiber optics.
Therefore, it is an object of the present invention to seal optical fibers to metal components in such a manner that the components are hermetic (measured helium leak rate of less than 1.times.10.sup.-8 cm.sup.3 /sec) and crack-free. The metal components will eventually be connected to other metal components in order to splice the optical fibers.
Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate the embodiments of the invention, and, together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to parts throughout the disclosure.